Shuso is a name for the position of the leader of ascetic monks in Zen sects. It is the highest position of the Rokuchoshu (six positions of lead monks). It is worshipfully called Choro (doyen) or Daiichiza (the first position). In the Rinzai sect, it is the name of a position and also the name of a priestly rank.
In the Zen sects, ascetic monks train mainly in training halls called "sodo." During the training periods in summer and winter called "seichu," monks concentrate on training and therefore cut off contacts with parties outside the temple. The leader of the monks during these periods is called "shuso."
The shuso, who is appointed by the chief priest prior to the seichu, is given a dedicated room separated from other monks and is requested to train more intensively.
Particularly in the Soto sect, the shuso is given a koan (question) on which the shuso must focus during the period of seichu. After the kaisei (end of a seichu period), the shuso, as a representative of the chief priest, must express his own spiritual state by answering questions related to Dharma from the other ascetic monks. This ceremony is called Hossen shiki (literally, Dharma combat).
In every Zen sect, executing the duty of shuso is one of the conditions under which to obtain qualification for being the chief priest. Currently, appointment to the shuso and the Hossen shiki are often performed for form's sake separately with the actual training.
Generally, one shuso is appointed during one seichu, but until the Edo period some of large priest halls had two shusos, which were the zendo shuso and godo shuso.